Evaporative emissions are hydrocarbon emissions, which are not from the exhaust. Evaporative emissions occur even when an engine, such an engine in an automobile, is not running. Sources of evaporative emissions include both fuel and non-fuel derived hydrocarbons. Non-fuel derived hydrocarbons are emitted by solvents, tires, carpet, glue etc. in an automobile and are typically only a new car problem. Fuel-derived hydrocarbon emission sources include the fuel tank, the engine, the exhaust gas recirculation (EGR) system and air intake system. In contrast to non-fuel derived hydrocarbon emissions, fuel-derived hydrocarbon emissions generally increase with time.
Increasing emissions regulations have led to an expansion of evaporative emission capture technology, and in particular, fuel-derived hydrocarbon emissions. It has been found that a significant amount of volatile hydrocarbons from several sources collect in the air intake system of the automobile engine after the engine has been shut off. Absent of an evaporative emission capture technology, these hydrocarbons are discharged into the atmosphere after the engine has been shut off. Thus, reducing or eliminating hydrocarbon emissions discharge in the air intake system is desirable.
A significant portion of a vehicle's evaporative emissions are emitted from the air intake system during the vehicle's off-cycle as a result of fuel injector leakage, residual fuel puddle evaporation, and blow-by gas from the positive crankcase ventilation (PCV) system. Ideally, the hydrocarbon emissions are retained with the air intake system until the powertrain is used again, when the emissions retention system releases the hydrocarbons to be consumed and controlled through the normal exhaust emission control systems.
Prior art solutions to controlling the outward flow of hydrocarbon emissions from air intake systems include careful shaping of the ducting and filter box; incorporation of carbon absorbents into the air intake system; and filters. A challenge for creating a hydrocarbon emissions absorber system is to minimize the impact on air intake restriction, add little extra weight to the system, and yet provide sufficient adsorption capacity for a particular application.
Accordingly, provided is a hydrocarbon adsorbent within the air intake system of a motor vehicle for adsorbing volatile hydrocarbons emitted after the engine has been shut-off, and thereby reduce or prevent the emission of such hydrocarbons into the atmosphere.